Trends in disk drive developments require an increase in the volumetric density of information storage and a reduction in the time required to access the stored information. One approach to increasing the density of information storage is to increase the number of disks in a given volume. This requires a reduction in the axial spacing of the disks which directly affects the design of the transducer suspension assembly, necessitating a reduction in its thickness. Increasing the number of disks increases the required number of transducers, load beams and arms for the actuator assembly, all of which add to the mass of or weight of, the actuator assembly, which supports, moves and positions the transducers. This is not consistent with a requirement for reducing the time required for accessing information on the disks.
A transducer suspension assembly conventionally comprises an arm connected to an actuator to be moved thereby. The distal end of the arm is connected to one end, called the mounting end, of a flexible or resilient load beam. A transducer, for example, a magnetic head, is flexibly supported on the distal end of the load beam in a position confronting the surface of the disk. In a disk stack of two or more disks, one arm of the actuator assembly will carry two such load beams in back-to-back relationship with the faces of the transducer confronting the adjacent surfaces of adjacent disks in the disk stack.
The load beams are fabricated of resilient stainless steel sheet which, in one form factor, are usually of the order of three mils in thickness. The load beams have channel or U-shaped cross sections. The mounting end of the load beam which is attached to the distal end of the arm, is fabricated with a reinforcing plate which is welded thereto. This reinforcing plate, which is used to mount the load beam, also has an essential reinforcement function for bending of the load beam, during the load beam fabrication process. This bend in the load beam is made to provide the required spring loading of the transducer against the surface of the disk, as is well known. Common practice in attaching the load beam to the arm is to screw the mounting end of the load beam to the arm through holes provided through the load beam and the reinforcing plate. See Robert B. Watrous U.S. Pat. Nos. 3,931,641 and 4,167,765. More recently, the reinforcing plate has been provided with a boss which fits into a hole in the distal end of the arm. See Coon et al U.S. Pat. No. 4,829,395 as an example. The bass is ball is bass is bass swaged in that hole to securely attach the load beam to the arm. The reinforcing plate, or swage plate, is an indispensable part of the load beam structure.
In such arrangements, the reinforcing plate (insert 132), which may be 20 mils thick, as stated by Coon et al, adds to the thickness of the actuator assembly at the point of its attachment to the distal end of the arm, which is a factor in any attempt to reduce disk spacing. Prior art practice, whether the load beam is attached to the distal end of the arm by means of screws or by ball swaging, according to the Watrous patents, supra, places the reinforcement plate between the load beam and the distal end of the arm. Thus the thickness of the actuator assembly at the distal end of the arm, which comprises the sum of the thickness of the arm, twice the thickness of a load beam, twice the thickness of a reinforcing plate, twice the thickness of a screw head, if screw attachment is used, and twice the clearance between a disk surface and the arm assembly at the distal end of the arm, determines the minimum axial spacing of the disks. There must be clearance between the disk and the arm assembly for mounting error tolerances and relative movement of the various structures during shock and vibration.
The patentees Coon et al, in U.S. Pat. No. 4,829,395, discuss the prior art arrangement aforesaid and, in an effort to achieve a reduction in disk spacing, disclose an arm structure to reduce the thickness of the actuator assembly, measured across the mounting ends of the load beams adjacent at the distal end of the arm, i.e., the load beam/arm attachment, by placing the load beam between the reinforcing plate (insert 132) and the arm. Then, by controlling the actuator assembly to prevent the reinforcing plates (inserts 132) from passing between the adjacent disks, the disk spacing may be reduced by twice the thickness of a reinforcing plate (insert 132). This, of course, assumes that the combined thickness of the two heads, their flexure mounts, the thickness of the distal ends of the load beams, and the clearance between the distal ends of the load beams, is less than the thickness of the actuator assembly at the load beam/arm attachment location.
FIG. 1 of this application illustrates a prior art structure of the type patented by Coon et al. Axially spaced disks 1 rotate about an axis 2. An arm 3 of an armstack structure, has a distal end 3a to which the mounting ends 4a of a pair of load beams 4 are attached. The distal ends 4b of the load beams 4 flexibly mount the transducers 5 which have faces which confront respective surfaces of the adjacent disks 1. A reinforcing plate, in this case a swage plate 6, is welded to the mounting end 4a of each load beam 4. A boss 6a is an integral part of each swage plate 6. The load beams are disposed against opposite faces of the distal end 3a of the arm 3, in which position the bosses 6a project into opposite ends of an opening 3b in the distal end of the arm 3. These bosses are ball swaged in the hole 3b to secure the load beams to the arm 3.
The swage plates 6 are shown in a position between the disks 1. According to Coon et al, if the swage plates 6 are prevented from passing between the disks, the disk spacing may be reduced a distance equal to twice the thickness of the swage plates 6. In that situation the disks need to clear only the load beams 4, since the swage plates 6 remain outside the peripheral edges of the disks 1.
As will be been by reference to FIG. 1 herein, using the Coon et al swage plate thickness of 20 mils, this spacing, from that required to clear the swage plates 6, may be reduced by 40 mils, providing the same disk clearance for the load beams as that which had been provided for the swage plates. A reductions in disk spacing by this approach, however, is limited by the axial dimension of the bosses 6a. The bosses must be of sufficient length to obtain and maintain a secure grip on the wall of the hole 3b. Additionally, clearance is required between the ends of the bosses sufficient to avoid end-to-end contact during swaging.
In a more recent prior art design, the bosses are designed so that one boss fits within the other within the hole in the arm. This is known as an interlocking swage. Ball swaging through the inner boss simultaneously secures the bosses together and secures the outer boss in the hole in the distal end of the arm. This reduces the thickness of the arm/load beam assembly.